1. Field of the Invention
The present invention relates generally to lasers, and more particularly, to external cavity lasers.
2. Related Art
The use of an external laser cavity with a spectrally selective element has been used for several decades to create a laser with a narrower spectral linewidth than is available with the non-wavelength selective mirrors in the laser cavity of the typical laser. In addition, the tenability of the spectrally selective element may create a laser with an agile wavelength that may be both narrow in line width and cover a broad tuning range. The spectrally selective element in many non-integrated external cavity lasers may be a diffraction grating. These diffraction gratings may be designed to meet a broad range of laser cavity needs such as size, efficiency, and dispersion. The tuning of the wavelength of the laser may be achieved by adjusting the grating angle of the diffraction grating with respect to the laser beam.
Tuning such a laser by merely adjusting the grating angle may result in the laser occasionally “hopping” from one cavity mode to another cavity mode. A cavity mode (referred to hereafter as a “mode”) refers to the integral number of half wavelengths of light at the tuned wavelength that fit within the optical cavity of the laser. Further, these hops from one mode to another are referred to as mode hops. Mode hops may result in the instability of the laser output by the laser system. Thus, it is desirable to reduce the number of mode hops that exist across a tuning range of the laser system.
Accordingly, there is a need for laser systems with improved mode hop performance over the tuning range.